I learn something new every single day and this is something so blindingly obvious that I can’t believe it hasn’t occurred to me before now. I was reading the entry about the Nymphalidae family of butterflies in my copy of Peter Eeles’s Life Cycles of British & Irish Butterflies when I came across this

the forelegs in both sexes are vestigial and useless for walking, and this family is sometimes referred to as the four-footed butterflies. The brush-like appearance of the forelegs has also resulted in the other common name for this family – the brush-footed butterflies.

Of course, I’d noticed that many species of butterfly sit on four legs (the skippers, for example, as well as most of the browns and the fritillaries, and the Red admiral pictured below) but I hadn’t realised that their forelegs are essentially useless for locomotion. And, indeed, according to an entry I’ve just read on Ray Cannon’s Nature Notes website, in some species of butterfly those forelegs have, during their long evolution, been adapted to function as sensory organs. Butterflies continue to amaze me!